Changed the argument names to base to be more informative in the repl.

Previously, `methods(base)` was less useful than it could be because all the variable names in all the methods are only single letters. This is especially true of `s` (now `symbols`).

Now, the first time an argument is used in one of the methods, it is given a full variable name. When an argument of the same type and purpose is used by another method, it is given just a single letter name. For example, `base` becomes `b`.

I also modified the documentation for `base` to reflect the change of name from `b` to `base`.